Various designs of apparatus for changing records, particularly in disc form, are known. The records employ a carrier or medium upon which information is stored for retrieval or playback. Typical examples of records include discs containing grooves of varying widths and depths for playback with a stylus, discs encoded for optical retrieval of information, such as compact discs and video discs, and other analogue and digitally encoded records. Information retrieval from records of particular interest to the invention is accomplished by rotating the record about a central axis and detecting a signal, such as an electrical signal or reflected light, that is converted to a useful information form.
In known changers, a record is selected from a library of records, some part or all of the information stored on the record is retrieved, and the record is returned to the library. Subsequently, a second record is selected, the desired information on that record is located and retrieved, and that record is returned to the library. Because of the construction of typical changers for records, there is an interruption or "dead time" between sequential information retrievals or playbacks from different records. The interruption begins at the end of information retrieval from a record, continues while that record is being returned to the library, while a new record is being selected from the library, and until the new record reaches its playback speed and the information desired to be retrieved is located on the record.
In audio and/or video record applications, the dead time prevents continuous retrieval of information from different records. Cross-fading from one record to another cannot be achieved. In data retrieval applications, valuable time is lost as a computer or other apparatus to which information is being supplied waits while records in the playback mechanism are being changed.
Several designs have been proposed to reduce the dead time between sequential information retrievals from separate records. For example, in Belgian Patent No. 898,775 a changer apparatus includes an annular magazine in which records are stored. A mechanism for selecting records from the magazine, for returning records to the magazine, and for playback of records is mounted on a circular plate within, and having a central axis coincident with that of, the magazine. Rotation of the plate positions the record selection and return apparatus opposite a selected disc for its retrieval and playback. However, some dead time occurs between the ending of playback of one record and the beginning of the playback of a second record. During that dead time, the first record is returned to one position in the magazine and the second record is selected from a different position in the magazine.
In a changer for magnetic tape cassettes disclosed in West German Auslegeschrift No. 21 16 028, playback mechanisms are provided on opposite sides of a magazine that rotates about a generally horizontal axis. That arrangement permits the selection of a cassette and the cueing of the tape in that cassette by one of the playback mechanisms while the other playback mechanism is retrieving information from a previously selected cassette. That changer avoids dead time interruptions between sequential information retrievals, but its design is difficult to apply to discs. Magnetic tape cassettes may be conveniently fitted with notches or other engaging means to aid selection, whereas circular discs cannot be similarly notched. Moreover, the circular shape of discs implies that a disc changer analogous to the German application tape cassette player would occupy a large volume. In that analogue, space for three side-by-side discs (one in each playback mechanism and one in the interposed magazine) would be required. Further, the cassette disclosed in the German patent publication is not suitable for use with discs. In a magazine rotating about a horizontal axis like that in the publication, discs are presented without discrimination between sides, and discs could be displaced from the magazine during rotation of the magazine about its axis.